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Subject[tip: x86/build] vmlinux.lds: Discard .note.gnu.property sections in generic NOTES
The following commit has been merged into the x86/build branch of tip:

Commit-ID: 72cb2113c1bbd82cf3e062a39ff2753ee9d3fae7
Gitweb: https://git.kernel.org/tip/72cb2113c1bbd82cf3e062a39ff2753ee9d3fae7
Author: H.J. Lu <hjl.tools@gmail.com>
AuthorDate: Fri, 27 Mar 2020 05:11:01 -07:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Fri, 27 Mar 2020 15:58:13 +01:00

vmlinux.lds: Discard .note.gnu.property sections in generic NOTES

With the command-line option, -mx86-used-note=yes, which can also be
enabled at binutils build time with

--enable-x86-used-note generate GNU x86 used ISA and feature properties

the x86 assembler in binutils 2.32 and above generates a program property
note in a note section, .note.gnu.property, to encode used x86 ISAs and
features. But the kernel linker script only contains a single NOTE segment:

PHDRS {
text PT_LOAD FLAGS(5);
data PT_LOAD FLAGS(6);
percpu PT_LOAD FLAGS(6);
init PT_LOAD FLAGS(7);
note PT_NOTE FLAGS(0);
}
SECTIONS
{
...
.notes : AT(ADDR(.notes) - 0xffffffff80000000) { __start_notes = .; KEEP(*(.not
e.*)) __stop_notes = .; } :text :note
...
}

The NOTE segment generated by the kernel linker script is aligned to
4 bytes. But .note.gnu.property section must be aligned to 8 bytes on
x86-64, resulting in:

[hjl@gnu-skx-1 linux]$ readelf -n vmlinux

Displaying notes found in: .notes
Owner Data size Description
Xen 0x00000006 Unknown note type: (0x00000006)
description data: 6c 69 6e 75 78 00
Xen 0x00000004 Unknown note type: (0x00000007)
description data: 32 2e 36 00
xen-3.0 0x00000005 Unknown note type: (0x006e6558)
description data: 08 00 00 00 03
readelf: Warning: note with invalid namesz and/or descsz found at offset 0x50
readelf: Warning: type: 0xffffffff, namesize: 0x006e6558, descsize:
0x80000000, alignment: 8

Since note.gnu.property section in the kernel image is never used,
discard it.

[ bp: Massage. ]

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200327121101.948934-1-hjl.tools@gmail.com
---
include/asm-generic/vmlinux.lds.h | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 2444336..998eafa 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -818,7 +818,14 @@
#define TRACEDATA
#endif

+/*
+ * Discard .note.gnu.property sections which are unused and have
+ * different alignment requirement from kernel note sections.
+ */
#define NOTES \
+ /DISCARD/ : { \
+ *(.note.gnu.property) \
+ } \
.notes : AT(ADDR(.notes) - LOAD_OFFSET) { \
__start_notes = .; \
KEEP(*(.note.*)) \
\
 
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